Multistage free piston motor compressor



July 7, 1936- H. JANICKE MULTISTAGE FREE PISTON MOTOR COMPRESSOR FiledMay 15, 1934 2 Shee ts-Sheet 1 In venfol:

July 7, 1936. H. JANICKE 2,046,631

MULTISTAGE FREE PISTON MOTOR COMPRESSOR Filed May 15, 1954 2Sheets-Sheet 2 Fig. 4-

ln ventor:

atented July 7, 1936 UNITED STATES MULTISTAGE FREE PISTON MOTORCOMPRESSOR Hermann Jinicke, Dessau, Germany, asslgnor to Hugo Junkers,Bayrisch-Zell, Oberbayern,

Germany Application May 15, 1934, Serial No. 725,749 In Germany May 20,1933 '11 Claims.

My invention relates to free piston motorcompressors and moreparticularly to apparatus comprising two pistons arranged in a cylindera the dimensions of the coupling gear care must be taken to avoid atransfer of mechanical energy by means of the coupling gear from oneside of the apparatus to the other. To this end in free piston,multi-stage compressors the two halves have been designed symmetricallyto each other, for instance by providing on each side a threestagecompressor, so that the apparatus comprises six stages. Such a device,however, has a very large overall length and is composed of a largenumber of parts. Even the scavenging pump'must be made in two parts, oneon each side, in order to avoid a unilateral load on the engine. If onthe other hand the structure is designed unsymmetrically, for instanceby arranging the scavenging pump at one side, or by providing differentnumbers of compressor stages on the two sides, the coupling gear willtransfer mechanical energy from one side to the other during the workingstroke and the return stroke, so that the members of the gear must bemade relatively strong and heavy. Hereby the weight of the reciprocatingmasses is increased, the building cost is high and owing to theincreased friction losses occurring in the coupling gear the efiiciencyis reduced.

It is an object of my invention to provide an unsymmetrical multistagefree piston motorcompressor of the kind referred to, in which thecoupling gear is substantially relieved from transferring mechanicalenergy from one side of the structure to the other. A device accordingto my invention involves the advantage that the overall length isconsiderably smaller than in symmetrically designed devices, while thecoupling gear may consist of light members. In order to accomplish thisI choose the pressure ratios or the volume ratios or both in the singlecompressor chambers in a suitable manner. In the multistage free pistonmotor-compressors hitherto known the ratios were so chosen that theamount of energy fed to the compressor chambers during the workingstroke or fed back to the free pistons during the return stroke isuniformly distributed over the single stages. In contradistinctionthereto in a structure according to my invention these energies aredistributed over the stages in a non-uniform manner, the sum of theenergies, however, on one side being equal to the sum of the energies onthe other side during the working stroke as well as during the returnstroke.

Other objects of my invention will appear from the followingdescription.

In the drawings afiixed to this specification and forming part thereofsome diagrams illustrating the operation of a motor-compressor accordingto my invention and an embodiment of such apparatus are showndiagrammatically by way of example.

In the drawings:

Figs. 1 to 3 are pressure-volume diagrams in which the abscissaedesignate the volume v and the ordinates the pressure p of the gas in acompressor stage.

Fig. 4 is an axial section of an apparatus according to my invention.

Referring first to Fig. 1, in which the curve B--CEG illustrates anoperating cycle of a compressor stage, the point B corresponds to theinner dead centre position of the piston of the stage. During theinitial portion of the working stroke, indicated by the curve BC, thegas is compressed from the pressure 111 to the pressure pa. During thelast portion of the working stroke, indicated by the horizontal straightline CE, the compressed gas is discharged. The energy fed to thecompressor stage during the working stroke may be calculated from thearea of the surface A-BC--EF-A. At the end of the working stroke a gasbody remains in the dead space or at the pressure 7):, in which isstored a portion of the energy fed to the stage during the workingstroke, this energy being re-fed to the piston of the stage during thereturn stroke in order to return the piston to its inner dead centreposition and to compress the charge of fuel in the motor cylinder of theengine. The return stroke is indicated in the diagram by the curve E-GB.During the initial portion E-G of the return stroke the gas body isexpanded from the pressure p: to the pressure p1. During the secondportion GB gas is sucked into the cylinder of the stage. The totalamount of energy fed back to the pistons during the return stroke may becalculated from the area of the surface A-B-GEF-A. The energy deliveredby the stage together with the discharged gas is rendered by the area ofthe surface enclosed by thecycle B-C-EG-B.

The energy fed to the stage during the working 5 stroke and thefeed-back energy fed back to the pistons during the return stroke, whichare rendered by the surfaces AB-c-E-F-A and ABGE-F A, respectively, are,fimctions of the pressure ratio I andotthevolumeratio on being thestroke volume.

Fig. 2 illustrates the diagram of a stage operatingatthesamepressureratioandthesame stroke volume, the volume ratio beinghowever increased by increasing the dead space from 01 to ur-I-v'r. Thecycle of this stage is illustrated by the curve BC'EG'. The energy ifedtothis stage during the working stroke is reduced with respect to thecorresponding value of Fig. 1 by the area of the surface BO-C'B, whilethe feed-back energy is increased by the area of the surface E-G-GE. Theenergy fed by the stage together with the discharged gas is indicated bythe area of the cycle BC'-EG' and is reduced with respect to thecorresponding vaiueoithediagramshowninFig. lbythesum of the areas of thesurfaces B -OC 'B and EG'-G-E.

Fig.3sbows adlagramofastageoperatingat a higher ratio and at the samevolume ratio and the same stroke volume as the cycle shown in Fig. l.The energy fed to the stage during the working stroke is increased bythe area of the surface CC" "-E and the feed-back energy is increased bythe surface of the area E"-G"GE".

Aswillbeseen fromthediagramsshownin Figs. 1 to 3, the energies fed tothe compressor stage during the working stroke and fed back by it duringthe retina stroke and the difierence V of these energies may be variedwithin wide limitsby suitably choosing the premure ratio and the volumeratio. Now in an unsymmetrically designed motor-compressor according tomy invention the pressure ratios and the volume ratios of the singlestages are so chosen as to obtain equal sums of energies on each sideduring the working sh'oke as well as during the return stroke, so thatthe coupling gear securing syn-' chronous reciprocation of the pistonsin opposite senses is relieved from transfer of energy exceptmg theenergy required for driving auxiliary devices such as fuel pinnps orcooling water pumps.

This shall be still further explained by discussing a three stage freepiston compressor comprising three compressor chambers, two of which arearranged on the same side of the structutre.

If the load is uniformly distributed over the stages by providing equalpressure ratios and vol- 'ume ratios therein, the side of the apparatuscomtwo stages would operate at two thirds, the other side at one thirdof the total load, so that the coupling gearing must transfer one sixthof the total load from one side to the other. If however, according tomy invention the pressure ratios on the side of the engine comprisingtwo stagw i. e. in. the embodiment shown in Fig. 4 onthelefthandside ofthe motorcylinder I are made smaller than the pressure ratio on theother side comprising only one stage, the energycanbeimiformlyoverbothsides. In consequence thereof a simpleconstruction comprising the minimum number of cylinders is obtained witha coupling gear relieved of transferofenergyandwhichmaybeconstmctedwith5 low weight members, the efliciency of the apparatus being increased byavoiding friction losses in the coupling gear. Instead of or besidesvarying the presure ratios, the volume ratios of the single stages maybe varied in a similar sense asdiscussedaboveinconnectionwiththepressure ratio. By varying the volumeratio the suction stroke 6-8 is reduced to GB (see Fig. 2).thusreducingtheamountotgcssuckedinduring thesuckingstroke.'Ihis,however,maybeeasily compensated for by gly increasing the diameterof the piston, which involves the further advantage that the diiferencebetween theforcesexertedbyoronthepistonawhichis amaximumattheendoftheworkingstroke, is IeducedbecausethisfomeiseuaItotheproductofthespeciflcpressure (p1 orpi) andthe area of the pistonsurface. In order to reduce this difference, the diameter; of thepistons of the stagesarrangedonthesidecom thesmaller numberofstagesshouldbeenlargedasfaras possible,andthiscanbedonebychoosingthevolume ratiointhesestageshigherthaninthe stages on the other side.

The amount of the forces exerted by the pis- 30 tons at the end of theworking stroke may be further controlled within certain limits bychanging thedischargeprossurem. pzhasaconstant value only, if thechamber into which the gas is discharged, has an infinite volume, sothat the pressureexistingthereinisnotbydisc arging the gas into the If,however, the chamber into which the gas is discharged from the stage, issuitably dimensioned, the discharge pressure pz will increase during thedischarge stroke, so that the corresponding portion of the diagram willbe indicated by a more or less inclined curve, as shown by CK in Fig. l,in which the discharge increases from in to p"z.

In some cases it may be desirable to increase the working surface of thepiston of a stage beyond the limit corresponding to the increase of thevolume ratio. In order to avoid in such cases an undesirable increase ofthe stroke volume and the'input and output of the stage, whereby theuniform distribution of energy would be disturbed, a portion of the gassucked in may be discharged during the portion of the working stroke, sothat the point 3 indicating the beginning of the compression is shiftedto the left along the line B-G shown inFig. i.

In an air compressor air ed from a low pressure stage during the portionof the working stroke in the manner described may be 60 added to thescavenging air conveyed by a scavenging pump. The pump may be formed bythe rear faces of one or a plurality of compressor pistons. If aseparate sca pump is provided,itshouldbe c f stages or energy storagechambers should be so chosen that the energy amounts fed to, and refedby, such chambers in addition to the energy amountsof the othercompressor stages amount to equal sums on the two sides of thestructure.

My invention may be used in connection with any free piston enginecomprising a multistage energy consumer, for instance a compressor, inwhich the stages are non-uniformly distributed over the sides of theapparatus. An example of such an apparatus is a three stage compressor,in which two stages are arranged on one side and one stage on the otherside. The invention may however be advantageously used also inconnection with compressors with an even number of stages, since indevices of this kind the areas of the diagram curves of the singlestages need not be equal, so that a compensation according to myinvention may involve considerable advantages in connection with thesedevices.

Referring now to Fig. 4 showing a three stage free pistonmotor-compressor, I is the motor cylinder and 2 and 3 are the motorpistons arranged in the cylinder I for synchronous reciprocation inopposite directions. 4 and 5 are scavenging and exhaust ports arrangedin the .wall of the cylinder and controlled by the pistons 2 and 3,respectively. The rod 6 of piston 2 is connected to the piston 3 of thefirst compressor stage, piston 8 being connected to the piston 2I of thethird stage. 9 and 22 are the cylinders, in which the pistons 8 and 2|reciprocate, respectively. Piston 3 is connected by means of rod I tothe piston III of the second compressor stage, which reciprocates in thecylinder I I. The freely moving bodies of the two sides of the apparatusare coupled with each other by means of a coupling gear. comprisingracks I2 and I2 and a pinion I3 rotataby securedto the casing of themotor cylinder by means of suitable bearings (not shown) or the like. IIare the suction valves of the first compressor stage, from whichcompressed gas is discharged through exhaust valves I5 into a connectingpipe I5, from which it is sucked by the second compressor stage throughsuction valves II. The air compressed in the second stage is dischargedthrough valves I8 into a connecting pipe I9, from which it is suckedthrough valve 20 into the third stage. The air compressed in the thirdstage is discharged through a pressure valve 23.

In order to equalize the energy amounts occurring on the two sides ofthe structure during the working stroke and during the return stroke,the pressure ratio and the volume ratio are chosen higher in the secondstage II, than in the other stages, in the manner discussed above. Theforces exerted by the pistons, particularly at the end of the workingstroke, are equalized by making the diameter of piston III relativelylarge. In order to avoid an undesirably large input of energy at thesecond stage, a portion of the gas sucked in is discharged again duringthe initial portion of the working stroke as described above,

pressure valves 24 being provided in the wall of the cylinders II,through which during the initial portion of the working stroke a portionof the gas sucked in through the valves I1 is re-fed into the pipe I5,until the piston III has passed the valves 24. Similar valves 25 may beprovided in the first compressor stage. The air discharged throughvalves 25 is used as additional scavenging air by providing a pipe 26connecting the valves 25 to the interior of the motor casing 33 used asa scavenging air container. The scavenging pump is' formed by the rearside of the piston 3 and by the portion of the cylinder 9 closed'by anend wall 29 provided with pressure valves 28. During the working strokethe scavenging pump sucks in air and discharges it during the returnstroke into the scavenging air container 33. The energy input and outputof the scavenging pump is balanced on the opposite side of the engine bya storage chamber connected with the second compressor stage and formedby the left-hand portion 32 of the cylinder II, which is closed by anend wall 3I. During the return stroke of the pistons the air present inthe chamber 32 is compressed and the energy amount therefor required maybe so chosen as to balance the energy demand of the scavenging pump.partial balancing may be obtained, if the wall 3| is omitted or isprovided with openings so that the chamber 32 is connected to theatmosphere and the piston I0, during its return stroke, must overcomethe pressure of the atmosphere. In any event the pressure ratios and thevolume ratios in the compressor stages 9, II and 22 and in the rearchambers 30 and 32 are so chosen that during the working stroke as wellas during the return stroke the sums of the energies are substantiallyequal on both sides of the engine, so

that the coupling gear I2, I2, I3is relieved from 35 transfer of energy.

The operation of the device shown in Fig. 4 is substantially the same asthat of known free piston devices. Fuel mixture is periodicallydelivered to the cylinder I through a fuel inlet 34 and burnt therein sothat the motor pistons 2 and 3 excute a working stroke, during which theair in the compressor chambers is compressed and partly discharged inthe manner above described. The pistons are returned to their inner deadcentre positions by the energy stored in the gas or air bodies remainingover in the dead spaces of the compressor chambers, scavenging beingeflected in the manner above described. It should, however, beunderstood, that in an apparatus according to my invention the pressureratios and the volume ratios are chosen in the manner described above soas to relieve the coupling gear from any substantial transfer of energyin spite of the fact, that the structure is not symmetrically designed.

I wish it to be understood that I do not desire to be limited to theexact details of construction shown and described for obviousmodifications will occur to a person skilled in the art.

I claim:

1. A free piston multi-stage motor compressor comprising in combinationa motor cylinder, a pair of pistons arranged in said cylinder andadapted to reciprocate therein in opposite directions, a coupling gearsubstantially free from transmitting mechanical energy connecting saidpistons for synchronizing the movements thereof, a plurality ofcompression cylinders, asymmetrically arranged on both sides of saidmotor cylinder, a compressor piston in each compression cylinder, eachcompressor piston and each compression' cylinder so determining theratios of the volumes and pressures prevailing in each compressioncylinder at the outer and inner dead center positions of said compressorpiston that, for the working stroke as well as for the return stroke,the sum of the work yielded in all compression cylinders on one side ofsaid motor cylinder is substantially equal to the sum or the workyielded in all compression cylinders on the other side of said motorcylinder.

2. A free piston multi-stage motor compressor comprising in combinationa motor cylinder, a pair of pistons arranged in said cylinder andadapted to reciprocate therein in opposite directions, :1 coupling gearsubstantially free from transmitting mechanical energy connecting saidpistons for synchronizing the movements thereof,

a plurality of compression cylinders arranged asymmetrically on bothsides of said motor cylinder, a compressor piston in each compressioncylinder, rigid connections connecting each motor piston with thecompressor pistons on its side of the motor cylinder, each compressorpiston and each compression cylinder so determining the ratios of thevolumes available in each compression cylinder at the outer and innerdead center positions. of said compressor piston that, for the workingstroke as well as for the return stroke, the sum of the work yielded inall compression cylinders on one side of said motor cylinder issubstantially equal to the sum of the work yielded in all compressioncylinders on the other side of said motor cylinder.

3. A free piston multi-stage motor compressor comprising in combinationa motor cylinder, a pair of pistons arranged in said cylinder andadapted to reciprocate therein in opposite directions, a coupling gearsubstantially free from transmitting mechanical energy connecting saidpistons for synchronizing the movements thereof, a plurality ofcompression cylinders arranged asymmetrically on both sides of saidmotor cylinder, a compressor piston in each compression cylinder, meansconnecting each motor piston with the compressor pistons on its side oi.the motor cylinder, said compressor piston and said compression cylinderso determining the ratios of the pressures prevailing in eachcompression cylinder at the outer and inner dead center positions ofsaid compressor piston that, for the working stroke as well as for thereturn stroke, the sum of the work yielded in all compression cylinderson one side of said motor cylinder is substantially equal to the sum ofthe work yielded in all compression cylinders on the other side of saidmotor cylinder.

4. A free piston multi-stage motor compressor according to claim 2, inwhich the ratios of the initial and end pressures prevailing in saidcompression cylinder at the outer and inner dead center positions ofsaid compressor'piston are substantially higher on the side oi. themotor cylinder comprising the smaller number of stages than on the otherside.

5. A free piston multi-stage motor compressor according to claim 2, inwhich the ratios of the initial and end volumes available in saidcompression cylinder at the outer and inner dead center positions ofsaid compressor piston are substantially higher on the side of the motorcylinder comprising the smaller number of stages than on the other side.

6. A freepiston multi-stage motor compressor comprising in combination amotor cylinder, a pair of pistons arranged in said cylinder and adaptedto reciprocate therein in opposite directions, means substantially freefrom transmitting the motor cylinder,

mechanical energy connecting said pistons for synchronizing themovements thereof, a plurality of compression cylinders arrangedasymmetrically on both sides or said motor cylinder, a compressor pistonin each compression cylinder, valve means associated with at least oneof said compression cylinders for discharging, during the initialportion of the compression stroke, a portion of the gas contained insaid compression cylinder, rigid connections connecting each motorpiston with the compressor pistons on its side of each compressorpistonand each compression cylinder so determining the ratios of thevolumes and pressures prevailing in each compressor cylinder at theouter and inner dead center positions of said compressor piston that,for the working stroke as well as for the return stroke, the sum of thework yielded in all compression cylinders on one side of said motorcylinder is substantially equal to the sum of the work yielded in' allcompression cylinders on the other side of said motor cylinder.

7. A free piston multi-stage motor compressor comprising in combinationa motor cylinder, a pair of pistons arranged in said cylinder andadapted to reciprocate therein in opposite directions, a coupling gearsubstantially free. from transmitting mechanical energy connecting saidpistons for synchronizing the movements thereof, a plurality ofcompression cylinders arranged asymmetrically on both sides of saidmotor cylinder, a compressor piston in each compression cylinder, saidcompression cylinders comprising high pressures and low pressuresstages, means in at least one low pressure cylinder for discharging,during the initial portion of the compression stroke, a portion of thegas contained in said cylinder and for delivering said portion to said,motor cylinder for scavenging purposes, rigid connections connectingeach motor piston with the compressor pistons on its side of the motorcylinder, each compressor piston and each compression cylinder sodetermining the ratios of the volumes and pressures prevailing in eachcompressor cylinder at the outer and inner dead center positions of saidcompressor piston that, for the working stroke as well as for the returnstroke, the sumof the work yielded in all compression cylinders on oneside of said motor cylinder is substantially equal to thesum of the workyielded in all compression cylinders on the other side of said motorcylinder.

8. A free piston multi-stage motor compressor according to claim 1 whichcomprises in combi-- nation a motor cylinder, a plurality of compressioncylinders and pistons provided therein, at least one of said cylindersbeing adapted to be used, on one side of the piston reciprocatingtherein, as a compressor chamber and on the other side as a scavengingpump, and valves connecting said pump with said motor cylinder.

'9. In a free piston multi-stage motor compressor according to claim 1,comprising a motor cylinder and a plurality of compression cylinders,the improvement which comprises means for adapting a compressioncylinder on one side of said motor cylinder to act as a scavenging pump,and means for adapting a compression cylinder on the other side thereofto act as an energy storage chamber.

10. In a free piston multi-stage motor compressor according to claim 1comprising a plurality of compression cylinders, the improvement whichcomprises a discharging chamber, valves connecting at least one of saidcompression cylinders to said chamber for discharginggas thereto duringthe compression stroke, said chamber being adapted to gradually increasethe pressure of the gas contained in said compression cylinder duringthe discharge.

11. In a, free piston multi-stage motor compressor' according to claim1, comprising a motor cylinder and a plurality of compression cylinders,the improvement which comprises means for adapting a compressioncylinder on one side of saidmotor cylinder to act as an energy storage 5chamber.

HERMANN JAmcKE.

